Analytical threshold voltage model for ultrathin SOI MOSFETs including short-channel and floating-body effects

Abstract

Short-channel effects (SCE) in ultrathin silicon-on-insulator (SOI) fully depleted (FD) MOSFETs are analyzed and an analytical model for threshold voltage, including the kink effect, is presented. The proposed model accounts for (1) a general nonuniform channel doping profile, (2) the drain-induced V/sub th/- lowering enhancement resulting from the interaction of (a) impact ionization, (b) floating-body, and (c) parasitic-bipolar effects. Good agreement between the proposed model and experimental data is demonstrated. Impact ionization and floating-body effects dominate V/sub th/ lowering for drain voltages larger than V/sub dk//spl sime/B/sub i/./spl lambda//sub i//3, where B/sub i/ is the impact ionization coefficient, and /spl lambda//sub i/ is the impact ionization length, a structural parameter which, for a single-drain SOI MOSFET, coincides with the SCE characteristic length /spl lambda/.